Asteroids are sometimes called minor planets. Asteroid are lumps of rock orbiting the sun, largely in the asteroid belt between the orbits of Mars and Jupiter.

The fourth asteroid to be discovered in 1807 is Vesta, It is the only one bright enough to be seen without a telescope.

The Ceres is the first and largest asteroid, It is 936 km in diameter and was found on New Year's Day 1801. Since then thousands have been found. Twelve of them are more than 250km wide and 26 are larger than 200km diameter. As telescopes have improved, more and more small asteroids have been detected. There are probably about 100,000 asteroids larger than 1km in diameter. Some experts think there may be as several as 1.2 million.

Toutatiswas discovered in 1989. It's named after the Celtic god Toutatis, whose alias is used as an oath by the comic strip character Asterix the Gaul. Toutatis dimensions (4.6 by 2.4 by 1.9km). It passes Earth every 4 years and is one amongst the most important space objects to come close to us. On 9 November 2008 Toutatis came within 7,524,773km of Earth.

Astronomers believe that on average, 1 asteroid larger than 0.4km strikes Earth every 50,000 years. Some 65 million years ago a 10km diameter asteroid crashing to Earth may have been responsible for wiping out the dinosaurs. This would have caused a catastrophic blast, affecting the chemical composition of the atmosphere, the climate and destroying the plants and animals on which the dinosaurs fed. As recently as 1991 a small asteroid came innards 170,600km of Earth, the closest recorded near miss. An asteroid is predicted to pass as close as 119,678km on 30 Jan 2052.

Halley's comet:British astronomer Edmond Halley (1656-1742) was the first to prove that comets travel in orbits, which making it possible to calculate when they will next be seen from Earth. Halley predicted that the comet he saw in 1682 would return in 1759. It did return and was named in his honor. The regular 76-year orbit of Halley's comet means that we can find historical accounts of its appearances going back more than two-thousand years. They were often believed to foretell important events.

Date closest to sun

Observations

25 May 240 BC

Seen in China

10 October 12 BC

Trusted to mark the death of Roman general Agrippa

28 June AD 451

Trusted to mark the defeat of Attila the Hun

20 March 1066

William believed the comet was a sign of Imminent win at the Battle of Hastings over King Harold . The comet and battlefeature in the Bayeux Tapestry, made some years later.

9 June 1456

The defeat of the Turkish army wasthought to belinked to the comet by 'Papal forces'.

15 September 1682

Observed by Edmond Halley, who predicted its return

13 March 1759

The comet's first return, as predicted by Halley, justifyinghis calculations correct

16 November 1835

The American author Mark Twain was born this year. He always believed that his fate was connected to that of the comet and in 1910, soon after it reappeared, he died.

10 April 1910

There was panic as many sure the world would come to and end.

9 February 1986

The Japanese Suisei probe, Soviet Vega 1 and Vega 2 and the European Space Agency's Giotto space probes passed close to Halley's comet. Astronomers concluded that the comet is madeof dust held together by Carbon Dioxide ice water.

28 July 2061

Next due to appear

More than 20 comets return more regularly than Halley. The most frequent visitor is an Encke's comet, which was named after the German astronomer Johann Franz Encke (1791-1865). He calculated the 3.3 year period of its orbit in 1818. The closest a comet has ever come to Earth was more than 500 years ago. On 20 February 1491, the so-called comet of 1491 came within 1,406,220km of Earth.